1. Field of the Invention
The present invention relates to an improved sewing machine, and more particularly to an improved looper thread take-up structure of sewing machine, which is capable of very easily clearing up tangling thread.
2. Description of the Prior Art
In each sewing travel of a conventional sewing machine, the looper thread is taken up once by a take-up mechanism so as to automatically feed the thread and adjust the tightness of the looper thread. FIGS. 1 and 2 show the take-up mechanism which includes a set of take-up cam member 61 and a thread guiding member 62. The looper thread 63 is first passed from a thread reel (not shown) through a thread guiding eye 64 of the thread guiding member 62 and then conducted to a looper (not shown) to cooperate with the upper thread 65 passed through the stitching needle 66 for sewing. Referring to FIG. 3, the take-up cam member 61 is a one-piece member formed of two identically shaped cam plates 67 by burning and welding. The two cam plates 67 are spaced by a wheel rim 68 with smaller diameter to define a cam gap 69 for the thread guiding member 62 to pass there through. By means of the rotation of the take-up cam member 61, the path of the outer rims of the cam plates 67 rotating through the thread guiding member 62 is varied in height so as to take up the stitching thread.
The earlier take-up mechanism is hidden in the base seat (not shown) of the sewing machine and fixed on a lower shaft not shown ). Once the stitching thread is broken, the thread head will be wound and tangled on the rim between the two cam plates during continuous rotation of the take-up cam member. The take-up cam member is fixed in the base seat of the sewing machine so that it is impossible to detach the take-up cam member therefrom. Under such circumstance, it is necessary to use a thin artistic knife to clear up the tangling thread in a very narrow space. This is a task. In order to solve this problem, some manufactures try to mount the take-up mechanism beside the column of the sewing machine instead (as shown in FIGS. 1, 2 and 3 ). However, such improved structure only makes it easier to detach the take-up cam member 61 from the sewing machine. In such structure, the take-up cam plates 67 still form a one-piece member made by burning and welding. After the take-up cam member is detached, it is still very difficult to clear up the tangling thread from the very narrow wheel gap (having a width of only 2 mm ). When the thin artistic knife is extended into the very narrow wheel gap to cut off the tangling thread, it often takes place that the polished outer rim of the take-up cam member is incautiously cut by the sharp blade of the artistic knife. After the take-up cam member is mounted back onto the sewing machine for further operation, the cut formed on the polished outer rim tends to cut off the stitching thread. This leads to a more serious problem of higher ratio of broken thread. Therefore, it is not secure to use the artistic knife for clearing up the tangling thread.
Furthermore, no matter what kind of tool is used to clear up the tangling thread, it is very hard to operate the tool in the very narrow gap for removing the tangling thread. Therefore, it often takes a considerably long time (half day to one day) to clear up the tangling thread. During this period, the machine must be stopped. This greatly affects the production efficiency and results in great trouble in working. Therefore, it is necessary to provide a measure to solve the above problem.